Attic storage area is open to chimney

This is an upstairs attic storage area that I have decided to close in. It is or was open to the rafters so I have just added a ceiling and drywalling it in and now doing the mud part.

But another sidewall has about a 18 x 18 opening to rafter area where the chimney goes up. In there is mounted a transformer with a source of power which I have always assumed powers the door bells.

Several years ago, rats gone in up there and made a mess and they probably made entry through this opening, the ceiling area or a drain pipe that comes in at the floor. I think I have two problems to solve.

1. drain pipe...can I stuff insulation in the hole around the pipe and shoot some of that foam insulation to seal it?

2. How best to seal up this door bell transformer next to the chimney. chimney is not used...gas logs. I could either leave it as and build a trap door for access with 1x2s to frame it. Or, I could pull the power and transformer into the interior and close off the 18 x 18 hole all together.

Suggestions appreciated.

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Attic storage area is open to chimney

whatever you decide to do you should leave an access way from you storage under to that portion you have closed off. The requirement from the building codes I am under (yours may vary) requires a minimum rough opening of 22" wide x 30" high when located in a wall. This is required (in my area) if the enclosed area is more than 30 square feet and has a vertical height of 30" or more as measured from the top of the ceiling framing members to the underside of the roof framing members.

I would seal any penetrations with either fire retardant spray foam or rock wool insulation. Either will seal any opening to prevent the spread of fire.